White wood pulp for high grade paper manufacture



Patented June 9, 1931' UNITED STATES PATENT? OFFICE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO COMPANY,

/ 'OF BEBLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE WHITE WOOD PULP FOR HIGH GRADE PAPER MANUFACTURE No Drawing.

- This invention relates to an improved wood pulp derived more especially from kraft pulp and possessing not only the impor tant papermaking characteristics, including strength and tear resistance, of the kraft pulp from which it is derived, but further possessing a pure white color and far greater freedom from resins and ash content and a notably lower pentosan content than is derm ivation material. The novelproduct' of the diflicult task, which when accomplished by the use of a hypochlorite bleach liquor is accompanied both by high bleach usage and marked injury to the papermaking characteristics ofthe-fiber. The product of the present invention, however, is one which is produced by a special processing of the kraft pulp aimed at the preservation of the val- .uable papermaking characteristics of such 110 pulp while removing from the pulp so much of its coloring matter and other constituents as are undesirable from .the papermakers standpoint. The product of the present invention is not one which is of extraordinarily 5 high alpha cellulose content, for if it be-attempted to refine kraft pulp markedly in so far as concerns increasing its alpha cellulose content, it loses especially in such properties as strength, even though it may be improved in other respects, such as softness and stabil- 1ty. 4 In producing the product of the present invention, I proceed as follows. A, raw kraft pulp is subjected to the action of chlorine wa- 4 ter or to'hypochlorite bleach liquor, or to a Application filed November 18, 1930. Serial No. 496,566.

succession of such reagents, without visible and/or 'hypochlorite should be used in such amount that the pulp after treatment has a distinctly diiferent hue than the raw kraft pulp. For example, raw pulp may be treated at temperatures of from to 100 F. for two to six hours, as a 4% to 6% stock suspension in chlorine water containing 4% to 8% chlorine, based on pulp. During this treatment, the pulp assumes a deep orange color. The treated pulp is then washed free of treating reagent and reaction products. When the washed pulp is tested, it exhibits a lower lignin content than that present in the original pulp. Ligneous matter is thus removed from the pulp without injury to its papermaking characteristics.

.The washed pulp is then treated with an alkaline liquor simllar to the cooking liquor used, in the kraft process of fiber liberation, namely, one containing both caustic soda and sodium sulphide. Preferably, the liquor is one containing 2% to 4% alkali, calculated as caustic soda equivalent, but 40% of which alkali is present in the form of sodium sulphide. The pulp is suspended in this specific liquor as an 8% to 10% stock SLISPBIISIOII' at 50 to 70 0., forfrom one to four hours. During this treatment, the pulp is further freed from ligneous matter, but without impairing its papermaking characteristics. The pulp is then washed, at which stage it has a lignin content of from 1% to 1.5%, as against alignin content of from 5% to 7% in the raw kraft pulp. It is thus seen that the process thus far is directed largely at the seective removal from the pulp of ligneous matter, the initial treatment selectively removing some of the lignin and chlorinating the rest, and the second treatment being conducted in an alkaline solution under conditions to dissolve out the chlorinated ligneous -matter. The selective dissolving out of the chlorinated ligneous matter, as already in- 4o pen 46 pulp being used in the ticular amounts of both caustic soda and sodium sulphide. Such temperature conditions are conducive to the desired dissolving out action without the marked refining effeet on the fiber which might be accomsigned to efl'ect an extensive elimination of lignin from the ulp without appreciably affecting its alpha cellulose content or its strength and tear resistance characteristics. The alkaline-digested and washed pulp is now ready to be bleached. Bleaching, too, mustbe carried out in a special way, in order to arrive at my novel product. To this end, the ulp is subjected 'to a series of three indedent bleaching treatments. The first two bleaching treatments consist in maintaining the pulp for three to six hours as a 5% suspension in hypochlorite bleach liquors at 70 F., 3% calcium hy ochlorite based on rst treatment, 2% calcium hypochlorite based on pulp being used in the second treatment, and 0.5% caustic soda based on pulp being added to the bleaching liquors in each treatment. The

pulp is washed and thickened between the rst two treatments, and again washed and thickened after the second treatment. The third bleaching treatment consists in maintaining the fiber for four hours as a 5% suspension in a permanganate solution at 70 to 75 F., containing about 0.3% potassium permanganate based on pulp. At the 'end of this treatment, the pulp is washed, but it x has a light tan color because of residual manganese oxides clinging to the fiber. The oxides are completely removed by treating the pulp with a dilute sulphurous acid solu .tion and washing. The resultingproduct,

which is in pure-white condition, may be delivered to machines which form sheets ready for shipment.

The following table indicates the transformation effected upon the given kraft pulp in producing the product of the present invention "-k cient pentosans therein in a form imparting toughness or strength to the sheet, without developing the brittleness imparted to a kraft pulp when it is whitened for example, by successive treatments with sulphurous acid and hypochlorite bleach liquor.

WVhile the product of the present invention has been described as being derived more especially from kraft pulp, it may be derived from othersuitable alkaline-cooked wood pulps, for instance, the lon -fibered soda pulps obtained by eifecting ber liberation from coniferous woods in so-called soda cooking liquors.

What I claim is: a

1. A 'pui'e-white wood pulp derived from alkaline-cooked pulp as a raw material, possessing the strength and tear resistance of its derivation material, but being of lower pentosan and much lower resin content than its derivation material.

2. A pure-white wood pulp derived from alkaline-cooked pulp as a raw material, possessing the strength and tear resistance of its derivation material, being of lower pentosan and much lower resin content than its derivation material, and having a total cellulose content in excess'of, but 'an alphacellulose content only about equal to, its derivation material.

3. A pure-white wood pulp derived from kraft pulp as araw material and having the plished at higher temperatures or with a Product of higher concentration of alkali in solution. Kraft $535.5. 10 For instance, if the treatment of the pulp be carried out at higher temperature with the Color--- Brown. Pure white. solution of alkali hereinbefore described, say Tgfgil glfig g {g3 3 53358 90 to 100 C. or higher, it is found that 35 i-g 5&3 there is a marked sacrifice in the tear resist- Resins(%3--- .244 011-013 15 ance of the pulp, even though its Mullen or ggif iiiff ff 153 @3 3 pop strength is not appreciably affected. On Teamsistance 250- 10 I 250-270 the other hand, if the treatment of the pulp be carried out at temperatures lower than It IS t h 0hSeFVed that hh P fi those specified with the solution of alkali the Present 1 Y n,1n addltlon to hav ng 20 hereinbefore described, there is a less efi'ecthe p p m mg har cterlstlcs, lncludlng tive removal of lignin from the pulp and a Fitrehgth and F s 0f klaft p lp, I strong tendency to reduce the Mullen and 15 0f p h c010? and s F extremely tensile strength of the pulp; and there is W resln cohtehtfm fact bemg apt to be an increase in the alpha cellulose leslholls specks than IIIOSt hed sulphlte 5 content of the pulp to a point where it ap- P 1 011 the market It a a 1I 111 3h hlgher proaches the characteristics of a refined total cellulose content than the Q g P wood pulp. It is thus seen that the treatbut Its alpha Cellulose hh h 1S Practlcauy ment of the pulp with a solution of alkali to the Same as that I the Orlglhal P P- produce the product of the present invention pentosan l h 1S somewhat wer han 30 is conducted within a temperature range de-- that of the ol'lglhal P p but there are to 89%, a copper number of from 1.0 to 2.0, (d) an ash content of from 0.1% to 0.3%, e; a resin content of from 0.1% to 0.3%,

f a. pentosan content of from 3.0% to 5.0%,

g) and possessing the strength and tear reslstance of the kraft pulp from which it; is derived.

In testimony whereof I have aflixed my Signatm' GEORGE A. RICHTER. 

